Mark has argued points of public importance involving Competition law before the Supreme Court: CMA v Flynn Pharma [2022] UKSC 14 (costs orders against the CMA); Sainsbury’s Supermarkets v Visa and Mastercard [2020] UKSC 24 (overcharge and pass-on); Deutsche Bahn v Morgan Crucible [2014] UKSC 24 (graphite cartel and time-bars); BCL Old v BASF [2012] UKSC 45 (vitamins cartel – meaning of infringement decision).

Cases involving important points of Competition law in the Court of Appeal include: CMA v Pfizer [2020] EWCA Civ 339 (test for excessive pricing); AB Volvo v Ryder Ltd [2020] EWCA Civ 1475 (immunity applicants and abuse of process); CMA v Concordia [2018] EWCA civ 1881 (search warrants and public interest immunity): Enron Coal Services v EWS [2011] EWCA Civ 2 (binding findings of fact in infringement decision); Argos v OFT [2006] EWCA Civ 1318 (tri-angular concerted practice).

Mark has appeared regularly before the Courts in Luxembourg and retains rights of audience as a member of the Irish bar. He appeared in the seminal case of Case C-453/99 Courage v Crehan (establishing the right to claim damages for breach of competition law); also, Case C-588/16P: Generics v Commission (pay for delay); Case C-457/10P AstraZeneca v Commission (regulatory abuse of dominant position); Case T-251/12 Freight Forwarding v Commission (price fixing cartel).

Mark has appeared in numerous trials involving competition law and many have given rise to important issues of competition law. They are referred to above, for example the interchange fee litigation. Others include: HG Capital v CMA (generic pharmaceutical pricing) Lexon v CMA [2021] CAT 5 (meaning of object infringement); Imperial Tobacco v OFT [2011] CAT 41 in the CAT (vertical price restraints); Hays v OFT [2011] CAT 29 (recruitment consultant cartel; reduction of penalty); Kier v OFT [2011] CAT 33 (construction cartel: reduction of penalty).

In addition to appearances in the CJEU Mark advises on competition law issues abroad. He appeared in the Supreme Court of Mauritius in Case 2017 SCJ 294 Emtel v Cellplus (margin squeeze in telecommunications) and was successful defending against the resultant appeal heard in the Privy Council in 2024.

Mark is currently acting in the trucks’ cartel litigation, in claims by Epic against Apple and Google, in several pharmaceutical cases involving pay for delay, and in the Libor litigation.

Competition: “He is good at delivering simple messages, really user-friendly and a really lovely man to deal with.” “Mark is a great tactician, thought leader and brings tremendous expertise to the table. He is always courteous and very approachable despite his level of seniority.” “His advocacy skills and ability to read a courtroom are phenomenal.” – Chambers UK, 2025

Leading silk in Competition: “Mark is undoubtedly at the top of the competition litigation Bar. His knowledge of the law is impressive, his written advocacy is straight forward and persuasive. Mark’s oral advocacy is understated but he has an uncanny ability to alight upon the most persuasive and important points.” – Legal 500, 2025

Competition: “He has amazing judgement.” “Mark is hugely strategic, very user-friendly, and has an encyclopaedic knowledge of the law.” “There is nothing that Mark doesn’t know about competition law.” – Chambers UK, 2024

Leading silk in Competition: “Mark is a great strategic thinker who brings leadership and insight to the most complex of cases.” – Legal 500, 2024

Competition: “He is an understated advocate but can be very effective in persuading the court. He is also very responsive, calm and considered, authoritative and great to work with.” – Chambers UK and Chambers Global, 2023 

Leading silk in Competition: “Mark is a leader in his field and offers a level of strategic insight into cases that is unmatched.” – Legal 500, 2023

Recommended in Competition, Who’s Who Legal Global Guide 2022

Recommended in Competition, Who’s Who Legal UK Bar 2022

Competition: “He is in most of the high-profile cases; he has huge experience. One of his strengths is that he can separate the good points from the bad and zoom in on the good ones.” “He is first class – good at persuading the judges.” – Chambers UK and Chambers Global, 2022

Leading silk in Competition: “Mark has an encyclopedic knowledge of competition litigation (he literally wrote the book) and this knowledge, combined with a commercial and tactical approach and user-friendly style makes him one of the top silks in this area.” – Legal 500, 2022

Recommended in Competition, Who’s Who Legal 2022

Competition: “He has fantastic judgement and really gets to the nub of his cases.” “He has the ability to translate very complicated and difficult areas of law into language that lay people can instantly understand.” – Chambers UK and Chambers Global, 2021

Leading silk in Competition: ‘‘A highly respected and well liked competition specialist.’’ – Legal 500, 2021

“Standout advocate who ranks highly for his impressive work representing clients before regulatory authorities and competition tribunals.” – Competition, Who’s Who Legal UK Bar 2020

Competition: “He has an understated advocacy style” and a “really good nose for how a case should be run.” “In court you can tell that all of the senior competition judges trust his views.” “He breaks down complicated issues for the judge to understand” and “you see all levels of the judiciary paying a lot of attention to him.” – Chambers UK and Chambers Global, 2020 

Leading silk in Competition: ‘‘Highly respected.’’ – Legal 500, 2020

“Ranks highly this year for his extensive experience appearing before English and Welsh courts, as well as the Competition Appeal Tribunal and the Court of Justice of the European Union” – Competition, Who’s Who Legal UK Bar 2019

Competition: “He has a very powerful instinct for the points that will appeal to a court and an attractive way of presenting arguments in court.” – Chambers UK and Chambers Global, 2019

Leading silk in Aviation: ‘‘Very knowledgeable, is a pleasure to work with and well-liked by clients’’ – Legal 500, 2018

Leading silk in Competition: ‘‘A pleasure to work with and well-liked by clients, he has an impressive ability to tailor his advice to his audience, often delivering complex advice with admirable brevity.’’ – Legal 500, 2018

Competition: “He has a finely tuned sense of what will play well and an excellent sense of how best to present points.” – Chambers UK, 2018

Leading silk in Aviation: ‘‘First-rate.’’ – Legal 500, 2017

Leading silk in Competition: ‘‘He marries expert knowledge with on-point analytical skills.’’ – Legal 500, 2017

“Displays all-round excellence in court and in conference.” – Chambers & Partners, 2017

“Excellent on his feet, clear-thinking and user-friendly.” – Chambers & Partners Global, 2016

“A first-rate individual.”  – Legal 500, 2016

“Tremendous; one of the top subject matter experts.” – Legal 500, 2016

“He “brings to the conduct of any case an intellectual originality that combines market-leading legal expertise with flair,”” – Chambers & Partners, 2013

“easy to work with and enormously impressive” – Legal 500, 2012

“Another standout silk at the set is Mark Brealey QC. He attracts strong praise from sources for his “pragmatic and commercial” approach and for the fact that he is “collegiate in his approach and a very good team player.”” – Chambers & Partners, 2012

“Mark Brealey QC ‘leads in competition law damages claims’ and ‘demonstrates an intelligent and balanced approach that attracts both judges and clients’” – Legal 500, 2011

“Mark Brealey QC impresses as one of the most popular barristers for both competition and EU law. “His reputation as a superbly clear and concise advocate is richly deserved,” sources say.” – Chambers & Partners, 2011

“A leading figure in follow-on damages cases, Mark Brealey QC has had ‘a number of recent successes’” – Legal 500, 2010

“Mark Brealey QC is “a subtle advocate who commands the respect of the court.”” – Chambers & Partners, 2010

“The ‘formidably intellectual, imaginative and compelling” advocate Mark Brealey QC’” – Chambers & Partners, 2010

“Mark Brealey QC offers ‘lateral thinking’”  – Legal 500, 2009